Head mounted display with micro-display alignment mechanism

ABSTRACT

A head mounted display device includes a structural frame arranged generally along a X-axis and a Y-axis for viewing along a Z-axis, the X, Y, and Z axes being mutually perpendicular. A micro-display is coupled to the structural frame, and configured to project visual content in a substantially forward direction along the Z-axis away from a user. A group of one or more optical elements with reflective optical surfaces is coupled to the structural frame and respectively positioned on a front side of the micro-display to reflectively guide a light ray bundle from the micro-display to a user&#39;s eye. A micro-display alignment mechanism is mounted to the structural frame and configured to align and control the reflectively guided light ray bundle from the micro-display to the user&#39;s eye by positioning the micro-display along the X and Z axes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility patent application claims priority to U.S. ProvisionalPatent Application No. 61/799,017, filed Mar. 15, 2013, which isincorporated herein by reference. This Utility patent application isrelated to U.S. Utility patent application Ser. No. 13/510,423 PCT filedon Nov. 21, 2009 and §371 date of May 17, 2012, and Utility patentapplications filed on even date herewith having Ser. No. 13/213,996entitled “Head Mounted Display Having Alignment Maintained ViaStructural Frame”, Ser. No. 14/214,330 entitled “Head Mounted DisplayWith Non-Pupil Forming Optical Path”, and Ser. No. 14/213,346 entitled“Head Mounted Display Assembly”, all of which are incorporated herein byreference.

BACKGROUND

Head mounted display (HMD) devices are employed for displaying andviewing visual content from a visual display source. An HMD device isconfigured to be worn on a user's head. An HMD device typically has (1)a single small display optic located in front of one of the user's eyes(monocular HMD), or (2) two small display optics, with each one beinglocated in front of each of the user's two eyes (bi-ocular HMD), forviewing a wide range of visual display content by a single user. Abi-ocular HMD allows for the possibility that the user may view visualcontent in 3-dimensions. The HMD devices that can currently be found intoday's military, commercial, and consumer markets are primarilygoggles/eyeglasses type devices that are worn the way a pair of gogglesor eyeglasses are worn, or they are helmet-mounted devices that areattached to a helmet that is worn on the user's head. Additionally, theHMD devices that can currently be found in today's market primarily relyon three different technologies, and thus typically fall into threedifferent categories: refractive; diffractive; and laser writer.

A first category of HMD devices currently found on the market is therefractive HMD. Refractive HMD's use the optical physics principle ofrefraction in order to transmit the projection of visual content from avisual display source to a user's eye. Refractive HMD's work bytransmitting a projection of visual content from a display sourcethrough a light transmission medium, typically a transparent plasticsuch as acrylic, to produce a final coherent and often magnified imageto the user's eye. The light transmission medium is essentially a lensor series of lenses that bend and magnify the light waves from thevisual source as they enter and exit the transmission medium so as toform the magnified cohesive image, similar to the operation of amagnifying glass. This is the dominant methodology employed in mostHMD's on the market today.

While the refractive HMD may be the dominant methodology used in the HMDmarket, it does have several drawbacks. The problem with such refractiveHMD's is that, with the transmission medium typically being large blocksof heavy plastic located in the optical path of the HMD, this type ofHMD is very heavy, bulky, and cumbersome for a user to wear on eitherhis head or face. This limits the overall comfort for the user wearingsuch an HMD. In addition, such a bulkier fit for the user significantlylimits the styling that may be applied to such a device. Furthermore,because the refractive lenses of refractive HMD's are often located inthe user's direct field of view, creating a refractive HMD that gives auser adequate “see-through vision,” or the ability to simultaneously seethe projected visual content and at the same time clearly see throughthe projected content to the real-world outside surrounding environment,a “mixed-reality” view, becomes very complicated. Another drawback ofrefractive HMD's is that they can often prevent a user from seeinganything other than the projected visual content or can severely limit auser's peripheral vision, which can ultimately leave the user feelingclaustrophobic. A further drawback of refractive HMD's is that, forthose commonly found in the consumer or commercial markets, they have avery limited field-of-view (FOV) angle, with the typical FOV being about25-degrees and the high-end FOV being about 40-degrees. When trying toincrease the FOV of refractive HMD's commonly found in the consumer andcommercial markets above the typical FOV of 25-degrees, the cost andweight of the device increases dramatically, which can be a significantprohibitive factor in two already competitive markets. This situation isapparent in the military market where refractive HMD's with FOV'sbetween 40-degrees and 120-degrees are much more common, however aspreviously stated, they are extremely heavy and very expensive.

A second category of HMD devices currently found on the market is thediffractive HMD, or more accurately, a hybrid refractive/diffractiveHMD. Diffractive HMD's use the optical physics principle of diffractionand diffraction gratings as well as refraction in order to transmit theprojection of visual content from a visual display source to a user'seye. With this type of HMD, the projection of the visual content ispassed through both a transmission medium and a diffraction gratingcontained within one of the refractive transmission medium elements toproduce a final coherent and often magnified image to the user's eye.The light waves from the projected visual content that are passingthrough the transmission medium ultimately pass through or are reflectedfrom the diffraction grating, which serves to present a single coherentimage to the user. Various drawbacks to such hybrid HMD systems includebulkiness, high power light source requirements, and a limited field ofview. These all limit their utility for military and industrialapplications as well as their appeal for consumer applications.

A third category of HMD devices currently found on the market is thelaser-writer HMD. The laser-writer HMD uses a remote laser light engine,often including a triad of red, green, and blue lasers, and a set oflaser writers to bend and beam the laser lights, according to an inputvisual display signal, into a coherent visual image. The lasers andlaser writer are connected to a head mounted display unit by coherentfiber optic cable in order to transmit the images to the head mountedunit. The images are then projected from the coherent fiber optic cableonto the final viewing screen, typically a transparent lens in the HMDunit, for viewing by the user. One drawback associated with this type ofHMD is that the coherent fiber optic cable employed for such a system isvery expensive. Another downside to such HMD systems is that, as theimage comes out of the fiber optic cable, the head unit will still needsome type of refractive optic to magnify the image, which in turntranslates to a limited FOV and increased weight of the head unit.Furthermore, another downside related to laser-writer HMD's becomesapparent when using such a system to view visual content in 3D. To doso, the HMD system would typically either beam two distinct images tothe head unit at the same time over a single fiber optic cable, thus thehead unit would incorporate a beam splitter to separate the two imagesfor each eye, or the HMD system would employ a second laser systemworking simultaneously with the first laser system in order to producethe second image employed to deliver 3D visual content. In either case,this can become extremely expensive. An additional downside to thelaser-writer HMD device is that the power consumption to run such adevice is extremely high. Lastly, transmitting an image to the headmounted unit via fiber optic cables can be potentially problematic ifcare is not taken to observe minimum bend radius of the fiber opticcable. If the cable is bent at too tight a radius, this will result insignificant signal losses.

None of the above three categories of HMD systems that are availabletoday are capable of providing magnified coherent visual content forviewing by a user from a single device that is all at once inexpensive,lightweight, comfortable, and that can be considered a near-to-eye HMDdevice. Consequently, because of the shortcomings and problemsassociated with the three types of systems currently available, there isa need in the industry for a new type of HMD device that is fairlyinexpensive, lightweight, compact, comfortable, and is a near-to-eyedevice.

Optical Path

As discussed above, in HMD devices available today, the optical pathtypically involves refractive optics that are ineffective, heavy, and/orbulky. In augmented reality systems, optical see-through head-mounteddisplays (“OST-HMD's”) have been one of the basic vehicles for combininga computer-generated virtual scene with the views of a real-world scene.Typically, through use of an optical combiner, an OST-HMD maintains adirect view of the physical world and optically superimposescomputer-generated images onto the real scene. Compared with a videosee-though approach, in which the real-world views are captured bycameras, the OST-HMD has the advantage of introducing minimaldegradation to the real world scene or providing a more accurate view.Therefore an OST-HMD is typically preferred for applications where anon-blocked real-world view is critical.

Designing an OST-HMD that has a wide FOV, a low F-number (which, inoptics is also referred to as the focal ratio and is the ratio of thefocal length to the diameter of the entrance pupil), is compact, and isnonintrusive has been a great challenge. Designing such an OST-HMD hasbeen especially difficult to achieve with a non-pupil forming system,wherein the light rays from the image that enter the eye are essentiallyparallel, so an eye does not need to be located at a particular locationto see the image formed by the light rays. Such a non-pupil formingsystem is in contrast to pupil-forming systems wherein the light raysconverge to a definite point in space, and if an eye is positioned infront of or behind this point the image will not be visible. The typicaleyepiece structure of HMD's available today uses rotationally symmetriccomponents that are limited in their ability to achieve a low F-number,large eye relief, and wide FOV. Many methods have been explored toachieve an HMD optical system which fulfills the above highly desirablecharacteristics. These methods include: applying catadioptric techniques(techniques involving both refractive and reflective optics);introducing new elements, such as aspherical surfaces, holographicoptical components, and diffractive optical components; exploring newdesign principles, such as using projection optics to replace aneyepiece or microscope type lens system in a conventional HMD design;and introducing tilt and decenter, or even free-form surfaces (FFS).(see, e.g., H. Hoshi, et. al, “Off-axial HMD optical system consistingof aspherical surfaces without rotational symmetry,” SPIE Vol. 2653, 234(1996); and S. Yamazaki, et al., “Thin wide-field-of-view HMD withfree-form-surface prism and applications,” Proc. SPIE, Vol. 3639, 453(1999).).

Among the different methods mentioned above, free-form surfacesdemonstrate great promise in designing compact HMD systems. It ischallenging, however, to design a free-form prism based OST-HMD offeringa wide FOV, low F-number, and sufficient eye relief. Many attempts havebeen made to design HMD's using FFS's, particularly in designs based ona wedge-shaped prism (see U.S. Pat. Nos. 5,699,194; 5,701,202;5,706,136; and D. Cheng, et al., “Design of a lightweight and widefield-of-view HMD system with free form surface prism,” Infrared andLaser Engineering, Vol. 36, 3 (2007).). For instance, Hoshi et al.presented an FFS prism offering an FOV of 34° and a thickness of 15 mm.Yamazaki et al. described a 51° OST-HMD design consisting of a FFS prismand an auxiliary lens attached to the FFS prism. More recently, Cakmakciet al. designed a 20° HMD system with one free-form reflecting surfacewhich was based on rational radial basis function and a diffractivelens. (“Optimal local shape description for rotationally non-symmetricoptical surface design and analysis,” Opt. Express 16, 1583-1589(2008)). There are also several commercially available HMD productsbased on the FFS prism concept. For instance, Olympus released theirEye-Trek series of HMD's based on free-form prisms. Emagin carried Z800with the optical module WFO5. Daeyang carried i-Visor FX series (GEOMCmodule, A3 prism) products. Rockwell Collins announced the ProView SL40using the prism technology of OEM display optics.

Existing FFS-based designs have an exit pupil diameter that is typicallyin the range of 4 mm to 8 mm, with a FOV typically around 40-degrees orless. In the more recent designs, smaller micro-displays, typicallyaround 0.6″, were adopted, which employ a focal length of around 21 mmto achieve a 40-degree FOV. The reduced focal length makes it verychallenging to design a system with a large exit pupil, or the virtualaperture in an optical system. As a result, most of the designscompromise the exit pupil diameter. Thus, commercially availableproducts on average reduce the exit pupil diameter to being within arange of about 3 mm to about 5 mm in order to maintain an F-numbergreater than 4. There are a few designs that achieve a larger exit pupilby introducing additional free-form elements or diffractive opticalelements. For instance, Droessler and Fritz described the design of ahigh brightness OST-HMD system with an F-number as low as 1.7 by usingtwo extra decentered lenses and applying one diffractive surface. (U.S.Pat. No. 6,147,807). The existing work in the field of optics and HMD'sshows that it is extremely difficult to design an HMD having both a lowF-number (indicating a high magnification ratio) and a wide FOV.

Accordingly, it would be an advance in the field of optical see-throughhead-mounted displays to provide a head-mounted display which has a wideFOV and low F-number while also providing a compact, light-weight, andnonintrusive form factor.

Structural Support of Optical Components

An optical path for a HMD is defined by various optical elements thatare held in precision alignment. A problem is how to maintain precisionalignment of the optical path without undue weight and bulk. Someoptical systems try to accomplish optical alignment by integrating allof the optical surfaces into a single, monolithic element, whichcombines both the refractive and reflective optics for the system in asingle optical element. This is typically done using lens surfacescombined with prismatic optics having low internal reflection losses.These systems are heavy and bulky, and have additional manufacturing andassembly complications. Other optical approaches utilize individualoptical elements which must be accurately aligned, both radially andlongitudinally. Another approach utilizes a light waveguide, such as forexample optical fiber or rectangular waveguides, to try and controlalignment errors, which method ultimately provides very small FOV's.

A practical HMD needs to be small and light for user comfort, as in apair of eye glasses. Most eye glass frames are flexible and do notprovide precision alignment suitable for a HMD. What is needed is alightweight eye glass configuration that is capable of providing aprecision alignment to an optical path, and to accommodate multipleindustrial designs without affecting the support or alignment of theoptical elements.

Micro-Display Mechanism

An HMD includes an optical path between a display and a user's eyes. Eyecomfort and ease of use are of paramount concern with all HMD's. Theoptical path and its various design parameters are one aspect ofachieving eye comfort. However, there are many factors affecting eyecomfort beyond the optical elements themselves. Human factors are ofgreat concern in proper HMD design. People's eyes vary greatly from oneperson to the next, and even in the same person, from eye to eye. Thismakes it desirable to build in additional adjustments to the HMD tofacilitate maximum eye comfort. Two concerns are the accommodation fordifferent users of varying focal points, or eye focus, and varyinginterpupillary distances, or the distance between the center of thepupils of a user's two eyes. Thus there is a need in HMD systems for theability to make optical adjustments, both front to back and laterally,to account for differences among users in individual eye focal lengthsand interpupillary distances. Typical existing adjustments tend to bequite bulky. What is needed is a very compact and light focusingmechanism that can fit into a lightweight HMD.

HMD Structure and Assembly Process

Among other functions, a HMD defines an optical path between amicro-display and a user's eyes. Optical components should be in preciseregistration with respect to one another in order to provide anacceptable image to the user. At the same time the resultant HMD shouldbe compact and light to be acceptable to a user. The design should alsobe able to withstand a physical impact without adversely affecting thealignment of the optical components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a user wearing a bi-ocular embodiment ofthe primarily reflective-based head mounted display device.

FIG. 2 is a side view of an embodiment of the primarily reflective-basedhead mounted display device.

FIG. 3 is a perspective section-view of a bi-ocular embodiment of theprimarily reflective-based head mounted display device that utilizesfive reflective optical surfaces.

FIG. 3A is a perspective section-view of a bi-ocular embodiment of theprimarily reflective-based head mounted display device illustrating anembodiment of the path of reflection from the light-emitting visualsource to a user's eye in a five-reflector system.

FIG. 4 is a rear perspective view of an embodiment of the primarilyreflective-based head mounted display device.

FIG. 5 is a perspective view of an alternate bi-ocular embodiment of theprimarily reflective-based head mounted display device that utilizesthree reflective optical surfaces.

FIG. 6 is a perspective section-view of a bi-ocular embodiment of theprimarily reflective-based head mounted display device illustrating anembodiment of the path of light reflection from the light-emittingvisual source to a user's eye in a three-reflector system.

FIG. 7 is a side schematic view of an embodiment of the reflectiveoptical surfaces in a five-reflector head mounted display deviceillustrating an embodiment of the path of light reflection from thelight-emitting visual source to a user's eye.

FIG. 8 is a side schematic view of an embodiment of the reflectiveoptical surfaces in a three-reflector head mounted display deviceillustrating an embodiment of the path of light reflection from thelight-emitting visual source to a user's eye.

FIGS. 9A-9C are a progression of a perspective exploded views of anembodiment of the last reflective optical surface in communication withan embodiment of an adjustable transmission-loss layer, wherein theadjustable transmission-loss layer has increasing darkness or opacitylevels in each of FIGS. 9A through 9C.

FIG. 10 is a front isometric view of an exemplary head-mounted displayaccording to one embodiment.

FIG. 11 is a rear view of an exemplary head-mounted display according toone embodiment.

FIG. 12 is a plan or top view of an exemplary head-mounted displayaccording to one embodiment.

FIG. 13 is a side view of an exemplary head-mounted display according toone embodiment.

FIG. 14 is a schematic representation of an exemplary ray trace diagramin a head-mounted display according to one embodiment.

FIG. 15 is a schematic representation of an exemplary optical pathutilized in a head-mounted display according to one embodiment.

FIG. 16 is a rear isometric view of an exemplary structural frameutilized in a head-mounted display according to one embodiment.

FIG. 17 is a rear isometric view of two exemplary compound lens elementsutilized in a head-mounted display according to one embodiment.

FIG. 18A is an exploded isometric view of a micro-display holder beingassembled to a carriage according to one embodiment.

FIG. 18B is an exploded isometric view of the assembly of amicro-display mechanism according to one embodiment.

FIG. 18C is an isometric view of a micro-display movement mechanismaccording to one embodiment.

FIG. 18D is a rear view of a micro-display mechanism depicting theaction of an X-gear upon a micro-display holder according to oneembodiment.

FIG. 18E is an isometric view of a micro-display mechanism depicting aninternal mechanical constraint according to one embodiment.

FIG. 18F is a side view of a micro-display depicting the action of aZ-gear upon a micro-display holder according to one embodiment.

FIG. 19 is a flow chart representation of an exemplary process forassembling a head-mounted display according to one embodiment.

FIG. 20 is an isometric representation of an exemplary process forassembling an outer frame for a head-mounted display according to oneembodiment.

FIG. 21 is an isometric representation of an exemplary process forassembling optical components to a structural frame for a head-mounteddisplay according to one embodiment.

FIG. 22 is an isometric representation of an exemplary process forassembling a head-mounted display according to one embodiment.

FIG. 23 is a first bottom view of a structural frame showing tabs fromthe optical elements positioned within the notched datum positioningmounts of the structural frame according to one embodiment.

FIG. 24 is a second bottom view of a structural frame showing tabs fromthe optical elements positioned within the notched datum positioningmounts of the structural frame according to one embodiment.

DETAILED DESCRIPTION

While the present invention is capable of embodiment in various forms,there is shown in the drawings, and will be hereinafter described, oneor more embodiments with the understanding that the present disclosureis to be considered as an exemplification of the invention, and is notintended to limit the invention to the specific embodiments illustratedherein. Headings are provided for convenience only and are not to beconstrued to limit the invention in any way. Embodiments illustratedunder any heading may be combined with embodiments illustrated under anyother heading.

Various embodiments now will be described more fully hereinafter withreference to the accompanying drawings, which form a part hereof, andwhich show, by way of illustration, specific embodiments. However, thisinvention may be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. The following detailed description is not to betaken in a limiting sense.

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The phrase “in one embodiment” does not necessarilyrefer to the same embodiment, although it may. Furthermore, the phrase“in another embodiment” does not necessarily refer to a differentembodiment, although it may. Thus, as described below, variousembodiments may be readily combined without departing from the scope orspirit of the present disclosure.

In addition, as used herein, the term “or” is an inclusive “or”operator, and is equivalent to the term “and/or,” unless the contextclearly dictates otherwise. The term “based on” is not exclusive andallows for being based on additional factors not described, unless thecontext clearly dictates otherwise. In addition, throughout thespecification, the meaning of “a,” “an,” and “the” include pluralreferences. The meaning of “in” includes “in” and “on.”

Described herein is a primarily reflective-based head mounted displaydevice for displaying and viewing visual content from a visual displaysource.

According to the present disclosure, the reflective head mounted displaydevice includes a frame and at least one near-to-eye optics housingconnected to the frame. The optics housing and frame are configured sothat the optics housing may be positioned at least partially in front ofan eye of a user. The optics housing includes a light-emitting visualsource located within the optics housing for projecting visual content.The optics housing also includes a plurality of reflective opticalsurfaces disposed within the optics housing that are configured toreflect a projection of the visual content from the visual source intothe eye of the user.

Accordingly, the present disclosure is primarily and substantially areflective-based head mounted display device as opposed to a primarilyrefractive, diffractive, or laser-writer-based head mounted displaydevice. In this manner, the present disclosure may optionally be a fullyrefractor-less head mounted display device. By primarily using aplurality of reflective optical surfaces to transmit the visual contentto an eye of a user, the device may use air as the transmission mediumthrough which the reflections pass, as opposed to heavy transparentplastic. This aspect of the present disclosure has the benefit of makingthe device significantly more lightweight than any other deviceavailable. It also has the benefit and distinction of being the firstoperational, near-to-eye, primarily reflective-based head mounteddisplay device ever developed, as previous industry efforts to developsuch a reflective-based device have been unsuccessful. Another benefitof the present disclosure is that, because the device is primarilyreflective-based, the reflectors may be sized and positioned such thatall of the reflectors employed to project visual content from a visualdisplay source to a user's eye may be contained within a relativelysmall optics housing that is kept near-to-eye. Such a compact deviceeliminates the need for substantial and expensive remote systems, suchas is necessary for laser-writer-based devices.

In another aspect of the present disclosure, the frame is a wearable,head mounted frame and the optical surfaces are configured tocooperatively magnify the projection of the visual content so that thevisual content appears larger than the actual size of the visual sourcefrom which it is being projected. In addition, the device may include afirst near-to-eye optics housing connected to the frame that isconfigured to be positioned in front of a first eye of a user, as wellas a second near-to-eye optics housing connected to the frame that isconfigured to be positioned in front of a second eye of the user. Inthis manner, a bi-ocular head mounted display is achieved.

In another aspect of the present disclosure, the optics housing alsoincludes a substantially opaque primary transmission housing that isconnected to a substantially transparent secondary vision housing. Thesecondary vision housing is positioned in front of the eye of the userand is designed to allow a user to see there through. It includes afront dust cover and a outer dust cover that are both transparent. Thesecondary vision housing has a variably-adjustable transmission-losslayer in communication with the outer dust cover. This transmission-losslayer allows for the selectable adjustment of the amount oftransmission-loss of any light passing there through. Accordingly, auser may adjust the layer so that it is fully transparent to allowviewing of all of the light passing there through, is completely dark oropaque to prevent viewing of the light passing there through, or hasvarying levels of darkness to allow partial viewing of the light passingthere through.

In another aspect of the present disclosure, the plurality of reflectiveoptical surfaces includes a series of reflective optical surfacesincluding a first reflective optical surface, at least one intermediateoptical surface, and a last reflective optical surface. The lastreflective optical surface may be an interior surface of the outer dustcover. The visual content is projected from the visual source to thefirst reflective optical surface. The visual content is then reflectedto at least one intermediate optical surface, next reflected to the lastreflective optical surface, which is the interior surface of the outerdust cover, and lastly reflected into the user's eye. The user canselectably choose to view only the visual content by making theadjustable transmission-loss layer, located behind the last reflectiveoptical surface, completely dark, thus blocking out his view of theoutside surroundings through the outer dust cover of the secondaryvision housing. Alternatively, the user may selectably choose to have“see-through vision” and view both the visual content and the real timeoutside surrounding environment at the same time, a “mixed-reality”view, by setting the adjustable transmission-loss layer to have onlypartial darkness or opacity. In this manner, the user would then see thereflection of visual content overlaid onto their real world view of theoutside surrounding environment.

In yet another aspect of the present disclosure, the head mounteddisplay is able to achieve a large field of view with a very lightweightand compact reflective system. In one embodiment the field of view (FOV)can be more than 40 degrees in full overlap mode (left and right imageshave the same field of view) or more than 80 degrees in zero overlapmode (left and right view fields are unique to the left and right eyes,respectively). In another embodiment the field of view can be more than50 degrees in full overlap mode or more than 100 degrees in zero overlapmode. In yet another embodiment the field of view can up to 60 degreesin full overlap mode or 120 degrees in zero overlap mode. In yet anotherembodiment the field of view can be more than 60 degrees in full overlapmode or more than 120 degrees in zero overlap mode. The degree to whicha large FOV value can be realized with a lightweight and compact frameis unique to the present disclosure.

Other embodiments, objects, features and advantages will be set forth inthe detailed description of the embodiments that follows, and in partwill be apparent from the description, or may be learned by practice, ofthe claimed invention. These objects and advantages will be realized andattained by the processes and compositions particularly pointed out inthe written description and claims hereof. The foregoing Summary hasbeen made with the understanding that it is to be considered as a briefand general synopsis of some of the embodiments disclosed herein, isprovided solely for the benefit and convenience of the reader, and isnot intended to limit in any manner the scope, or range of equivalents,to which the appended claims are lawfully entitled.

HMD Device Construction

Referring to FIGS. 1, 2 and 5, a primarily reflective-based head mounteddisplay (HMD) device 5 for displaying and viewing visual content from adisplay source is disclosed. The HMD device 5 includes a frame 10 and atleast one near-to-eye optics housing 15 connected to the frame 10.

In one embodiment, the frame 10 is a wearable, head mounted frame suchas that of an eyeglasses frame. However, the disclosure of thisembodiment should not be read to limit the shape of the frame 10.Accordingly, in alternate embodiments the frame 10 may be of any typethat can be configured to be mounted to a helmet or mounted to any othersimilar type of head wearable device, such as a head band or adjustablehead strap. The frame 10 is connected to the near-to-eye optics housing15 and is configured to support the weight of the near-to-eye opticshousing 15. The frame 10 is also configured such that the optics housing15 may be positioned at least partially in front of an eye of a user andin the HMD user's line of sight when properly worn.

In one embodiment, the frame 10 is connected to two optics housings 15wherein a first optics housing 15 can be placed at least partially infront of a user's first eye and a second optics housing 15 can be placedat least partially in front of a user's second eye. The first and secondoptics housings 15 may be physically identical, mirror images of eachother, or other combinations of size and shape as may be desired. Thisembodiment is considered a “bi-ocular” HMD device because it is a devicethat utilizes two separate channels (i.e., the two separate opticshousings 15) to provide separate visual content to each of a user's twoeyes. Bi-ocular HMD devices can allow a user to view 2-dimensionalvisual content either by providing the exact same visual content overboth channels to both of the user's eyes at the same time (e.g., similarto watching a television), or by providing a first visual content over afirst channel to a users first eye and providing completely differentsecond visual content over the second channel to a user's second eye(i.e., like having each eye watch a separate television with eachtelevision showing different programs), or lastly by providing visualcontent over a first channel to only a user's first eye and notproviding any content to the user's second eye. Alternatively, bi-oculardevices can allow a user to achieve 3-dimensional stereoscopic vision(i.e., binocular vision) by providing each eye with a slightly differentversion of the same visual content. However, the disclosure of thisembodiment should not be read to limit the HMD device 5 to only deviceshaving two optics housings 15. Accordingly, in an alternate embodiment(not shown), the frame 10 may be connected to only one optics housing15, wherein the frame 10 and optics housing 15 are then configured suchthat the one optics housing 15 can be placed partially in front of auser's first eye. The device of this alternate embodiment is considereda “monocular” HMD device because it is a device that utilizes a singlechannel (i.e., one optics housing 15) for only one of a user's two eyes.

In yet another alternate embodiment (not shown), the frame 10 and opticshousings 15 may be configured such that the optics housings 15 areselectably attachable/detachable from the frame 10, thus allowing theuser to choose whether to utilize a monocular HMD device, having onlyone optics housing 15 for a single eye, or a bi-ocular HMD device,having two optics housings 15, one for each of the user's eyes. In stillanother alternate embodiment (not shown), the optics housings 15 may behingeably connected to the frame 10 such that the optics housings 15 canbe selectably rotated about a hinge to remove the optics housings 15from a location in front of the user's eyes and remove them from theuser's line of sight.

The frame 10 is comprised of at least one durable, lightweight materialsuch as a magnesium alloy, aluminum alloy, titanium, or any othersimilar lightweight metal based material that has the physicalproperties of being very lightweight yet very durable. However, thedisclosure of the aforementioned materials should not be read to limitthe lightweight materials to only metal-based materials. Accordingly, inalternate embodiments the frame 10 may be comprised of a durablelightweight material such as polycarbonate, PVC, polyethylene, nylon, orany other polymer based material that has the physical properties ofbeing very lightweight yet very durable.

Referring to FIGS. 3 and 5, each near-to-eye optics housing 15 includesa light-emitting visual source 20 for projecting visual content, aplurality of reflective optical surfaces 30, a primary transmissionhousing 40, and a secondary vision housing 45.

The light-emitting visual source 20 is an electronic device thatpresents information in visual form that is capable of being viewed byan observer. In a one embodiment, the light-emitting visual source 20 isa micro-display connected to a power source, wherein the micro-displayincludes a source input for accepting input signals from an externalsource, which are to be output in visual form. However, the disclosureof the aforementioned embodiment should not be read to limit the type oflight-emitting visual source(s) that may be utilized in the practice ofthe matter disclosed herein. Accordingly, in alternate embodiments, thelight-emitting visual source 20 can be a laser writer, micro-projector,or any other device or system that is capable of displaying visualcontent. Furthermore, the light-emitting visual source 20 may receivethe input signals from the external source via conventional wires orcables, fiber optics, wireless signal transmission, or any other similarway of transmitting signals known to those skilled in the art of signaland data transmission.

Visual content to be projected includes both static and dynamic visualcontent, and any additional content that can be visually displayed andis capable of being viewed. Static visual content includes content thatdoes not change over the time during which it is displayed and includesbut is not limited to photos, still imagery, static text and graphicdata displays that do not update with new information. Dynamic visualcontent includes content that does change over the time during which itis displayed and includes but is not limited to video playback or realtime video, changing imagery, dynamic text and graphic data displaysthat update as new information is obtained.

The plurality of reflective optical surfaces 30 are surfaces that have ahighly polished or smooth surface finish, such as that of a mirror,polished metal, or smooth glass for example, and use the optical physicsprincipal of reflection in order to cast back light waves that areincident upon them. The plurality of reflective optical surfaces 30 arein optical communication with the light-emitting visual source 20 andare configured to cooperatively reflect a clearly focused projection ofthe visual content from the light-emitting visual source 20 into the eyeof the user.

Referring to FIGS. 3A and 6, in one embodiment, the plurality ofreflective optical surfaces 30 are a combination of separate concave andconvex surfaces and include at least a first reflective optical surface31 and a last reflective optical surface 36. The first reflectiveoptical surface 31 is the reflective optical surface into which thevisual content is first projected from the light-emitting visual source20. The last reflective optical surface 36 is the reflective opticalsurface from which the visual content is last reflected into the user'seye. In one embodiment, the plurality of reflective optical surfaces 30also include at least one intermediate reflective optical surface (notshown). These concave and convex reflective optical surfaces 30 areadditionally configured to cooperatively magnify the projection of thevisual content when the projection is reflected off of each reflectiveoptical surface 30, so that the projected visual content 55 (FIGS.9A-9C) appears magnified and in focus when viewed by the HMD deviceuser's eye. However, the disclosure of the aforementioned embodimentutilizing a combination of separate concave and convex surfaces shouldnot be read to limit the scope of the shape of reflective opticalsurfaces that may be used in an HMD device as disclosed herein. Inalternate embodiments, the HMD device 5 may utilize solely convexreflective optical surfaces, solely concave reflective optical surfaces,or other unique geometries without departing from the scope of thedisclosure herein. Furthermore, although the disclosure of theaforementioned embodiments has thus far been directed to HMD's utilizingonly a plurality of reflective optical surfaces 30 to reflect the visualcontent projected from the visual source 20 to a user's eye, alternateembodiments may include additional optical elements incorporated intothe optical path without departing from the scope of the disclosure to aprimarily reflective-based HMD. Accordingly, in alternate embodiments,in addition to including a plurality of reflective optical surfaces 30,one or more refractive elements (not depicted) may be located in theoptical path between the light-emitting visual source 20 and the user'seye, in order to manipulate the light waves that will pass therethrough. In this regard, a hybrid reflective/refractive HMD is created.

Referring to FIGS. 2 and 4, each near-to-eye optics housing 15 includes,or has connected thereto, a diopter adjuster 25 that is in communicationwith the light-emitting visual source 20. The diopter adjuster 25 isconfigured to physically move the position of the light-emitting visualsource 20 either forward or backward, in a direction that issubstantially parallel to the direction of visual content projectionemanating from the light-emitting visual source 20. In doing so, thelight-emitting visual source 20 will move either closer to or furtheraway from the fixed location of the first reflective optical surface 31.This results in a corresponding adjustment to the final focal point ofthe projected visual content within the user's eye. Accordingly, thediopter adjuster 25 is able to provide prescription focus correction andadjust the focus of the visual content that is projected to the user'seye over a fixed prescription range.

Referring again to FIGS. 1 through 6, the primary transmission housing40 is a chamber of the near-to-eye optics housing 15 in the HMD device 5in which the projection of the visual content from the light-emittingvisual source 20 originates, and in which the majority of the opticalreflection and magnification of the projected visual content occurs. Inone embodiment, the primary transmission housing 40 is a substantiallyopaque, hollow chamber that has the light-emitting visual source 20 anddiopter adjuster 25 disposed at a first end 41 thereof. The primarytransmission housing 40 may further contain each of the plurality ofreflective optical surfaces 30 except for the last reflective opticalsurface 36, disposed at various positions inside of the primarytransmission housing 40. More specifically, the plurality of reflectiveoptical surfaces 30 are disposed, in part, either directly on the frontand rear internal walls of the primary transmission housing 40, or onsupport structures located on the front and rear interior walls of theprimary transmission housing 40. In one embodiment, the primarytransmission housing 40 is connected to and supported by the frame 10.However, the disclosure of the aforementioned embodiment should not beread to limit the structure of the primary transmission housing 40 toonly being a substantially opaque or hollow chamber. In alternateembodiments, the primary transmission housing may be an open sidedstructure or an open skeletal framework that simply serves to supportthe reflective optical surfaces 30, the light-emitting visual source 20,and diopter adjuster 25 in their appropriate locations, but that doesnot prevent outside incident light from entering into the reflectivepath of the reflective optical surfaces 30.

The primary transmission housing 40 is comprised of at least onedurable, lightweight material such as a magnesium alloy, aluminum alloy,titanium, or any other similar lightweight metal based material that hasthe physical properties of being very lightweight yet very durable.However, the disclosure of the aforementioned materials should not beread to limit the lightweight materials to only metal-based materials.Accordingly, in alternate embodiments the primary transmission housing40 may be comprised of a durable lightweight material such aspolycarbonate, PVC, polyethylene, nylon, or any other polymer basedmaterial that has the physical properties of being very lightweight yetvery durable. Furthermore, with regard to the position of the primarytransmission housing, in one embodiment, the primary transmissionhousing is configured to be substantially located below the frame 10 andthe user's eye, and adjacent to the user's face. However, in alternateembodiments, the primary transmission housing 40 may be configured to besubstantially located along the length of any earpiece associated withthe frame 10, adjacent to a side of the user's face, above the frame 10,above the user's eye, adjacent to the user's forehead, or at any otherlocation as needed that allows the HMD device disclosed herein tofunction according to the teachings disclosed herein.

Referring to FIGS. 2-4 and 6, the secondary vision housing 45 isconnected to the primary transmission housing 40 at a second, open end42 of the primary transmission housing 40, opposite the first end 41 inwhich the light-emitting visual source 20 is located. The secondaryvision housing 45 is the portion of the optics housing 15 that is placedat least partially in front of the HMD device user's eye. In oneembodiment the secondary vision housing 45 is also integrally connectedto the both the frame 10 and the primary transmission housing 40.However, the disclosure of the aforementioned embodiment should not beread to limit the secondary vision housing 45 to being integrallyconnected to either the frame 10 or the primary transmission housing 40.In an alternate embodiment, the secondary vision housing 45 can bedetachably or hingeably connected to and supported by the primarytransmission housing 40.

Referring to FIGS. 3-4 and 6, the secondary vision housing 45 includes atransparent front dust cover 46 that is configured to be positioneddirectly in front of the user's eye and in the user's line of sight. Inone embodiment, the front dust cover 46 is optically neutral, in that itdoes not act like a traditional prescription lens. Rather, the frontdust cover 46 allows light waves from any visual object being viewed bythe user to pass through it without any noticeable distortion,alteration, or bending thereof. Furthermore, in one embodiment the frontdust cover 46 is comprises a durable transparent material such aspolycarbonate, glass, acrylic, or any other similar material that isboth transparent and durable.

The secondary vision housing 45 also includes an outer dust cover 47,which is substantially a shell located adjacent to the front dust cover46. The outer dust cover 47 is configured to be positioned in front ofthe front dust cover 46 and positioned in the user's same line of sightas the front dust cover 46. Together, the front dust cover 46 and outerdust cover 47 of the secondary vision housing 45 serve to close off theopen, second end 42 of the primary transmission housing 40, and thussubstantially seal the optics housing 15 so as to prevent dust or anyother environmental contaminants from entering the optics housing 15 andinterfering with the reflective optics.

Referring to FIGS. 9A-9C, the outer dust cover 47 includes a concave,interior surface 48 that is configured to be the last reflective opticalsurface 36 among the plurality of reflective optical surfaces 30. Aspreviously disclosed, this interior surface 48 is the reflective opticalsurface 36 from which the projected visual content 55 is last reflectedinto the user's eye. In one embodiment the outer dust cover 47 is asubstantially transparent, curved shell that is in communication with avariably-adjustable transmission-loss layer 50. In this embodiment, theouter dust cover 47 is comprised of a durable transparent material suchas polycarbonate, glass, acrylic, or any other similar material that isboth transparent and durable. Furthermore, the outer dust cover 47 mayoptionally be designed to have a material thickness sufficient toachieve at least the minimum requirements for providing ballisticprotection in optical devices. However, the disclosure of theaforementioned embodiment should not be read to limit the outer dustcover 47 to being only a basic transparent or substantially transparentpassive shell. In alternate embodiments (not shown), the outer dustcover 47 may be a switchable mirror or a reversible electrochromicmirror or any other similar such technology that allows for selectivemirroring or adjusting of the reflectance of the outer dust cover 47.

In an additional alternate embodiment, the substantially transparentouter dust cover 47 may also be a “partial mirror,” in that theotherwise transparent outer dust cover 47 has a partially mirroredinterior surface 48, and thus a partially mirrored last reflectiveoptical surface 36. This partially mirrored interior surface 48 has afixed minimum reflectance value associated therewith. The reflectancevalue is a ratio, expressed as a percentage, of the total amount ofradiation, as of light, reflected by a surface, to the total amount ofradiation initially incident on the surface. Having a partial mirror asthe interior surface 48 of the outer dust cover 47, and thus the lastreflective optical surface 36, allows the HMD designer to increase theminimum reflectance value of the reflective optical surface above thatwhich would otherwise be achievable with the use of only an untreated,transparent outer dust cover 47. In such an embodiment, a partial mirrormay be created by having the interior surface 48 of the otherwisetransparent outer dust cover 47, as disclosed above, treated or coatedwith a thin deposit of a reflective material (i.e., aluminum, silver,gold, etc.) in order to enhance the interior surface's 48 reflectanceand create a minimum fixed reflectance value for the last reflectiveoptical surface 36. By selecting the proper type and thickness of thereflective material that is to be deposited on the last reflectiveoptical surface 36, a partial mirror having the desired minimumreflectance value may be accurately achieved. In one embodiment, apartial mirror may have a minimum reflectance in a range of about 1-10%,11-20%, 21-30%, 31-40%, 41-50%, 51-60%, 61-70%, 71-80%, 81-90%, or91-99%.

Because the substantially transparent outer dust cover 47 of oneembodiment is a curved shell having a concave interior surface 48, theouter dust cover 47 acts as a refractive lens that distorts the user'sview of the surrounding environment when viewed there through.Accordingly, an exterior surface 49 of the outer dust cover 47 has aseparate corrective refractive lens shape (not shown) formed thereonthat counteracts this distortion to result in an outer dust cover 47that is optically neutral with no noticeable distortional effectsoccurring to the light waves that pass there through.

Referring again to FIGS. 9A to 9C, in one embodiment, thevariably-adjustable transmission-loss layer 50 in communication with theouter dust cover 47 can selectably be made to have varying levels ofdarkness or opacity, ranging from completely dark or fully opaque tofully transparent. In one embodiment, the adjustable transmission-losslayer 50 may comprise at least three distinct layers 51, 52, 53, whereina flexible and adjustable liquid crystal layer 52 is laminated orlocated between two protective layers 51, 53 (see FIGS. 9A to 9C). Thissandwich of three layers can be removably attached to either theexterior surface 49 or interior surface 48 of the outer dust cover 47and the darkness of liquid crystal layer may be adjusted to allow forvarious levels of transmission-loss of the light that passes therethrough.

However, the disclosure of the aforementioned embodiment should not beread to limit the adjustable transmission-loss layer 50 to being aseparate removable layer that can be attached to the outer dust cover47. In alternate embodiments, the adjustable transmission-loss layer 50may be integrally associated with the outer dust cover 47. In such anembodiment, the outer dust cover 47 may comprise at least two separatelayers, wherein the adjustable transmission-loss layer 50 is a flexibleand adjustable liquid crystal layer that is laminated or located betweentwo of the layers of the outer dust cover 47. In yet another alternateembodiment, the adjustable transmission-loss layer 50 may be integrallyassociated with the exterior surface 49 or interior surface 48 of theouter dust cover 47. Additionally, the disclosure of the aforementionedembodiments should not be read to limit the adjustable transmission-losslayer 50 to only using liquid crystal technology. In alternateembodiments the adjustable transmission-loss layer 50 may utilize anytype of technology or be any type of layer that is capable of attainingadjustable levels of transmission-loss, such as switchable mirrors orreversible electrochromic mirrors.

In addition, because the front dust cover 46 and outer dust cover 47 ofone embodiment are substantially transparent, the user has the abilityto see through both the front dust cover 46 and the outer dust cover 47,so as to view both the user's real-world surrounding environment and, atthe same time, view the projected visual content 55 overlaid onto theuser's view of the real-world surrounding environment. This provides theuser with “see-through vision” in which the user simultaneously sees amixed-reality view of both the visual content 55 and the surroundingenvironment. If the user wants a brighter view of the projected visualcontent 55, he can increase the level of darkness or opacity associatedwith the adjustable transmission-loss layer 50 further towards the darkor opaque end of the scale, which in turn will increase thetransmission-loss of outside light passing through the layer to theuser's eyes, and darken the view of the surrounding environment that theuser is able to see. If the user makes the adjustable transmission-losslayer 50 completely dark or opaque, he will only be able to see theprojected visual content 55, and the outside environment will becompletely blocked out. If, however, the user adjusts the adjustabletransmission-loss layer 50 to be fully transparent, the user will stillbe able to see a faint projection of the visual content 55 while havinga bright view of the surrounding environment. In one embodiment in whichthe outer dust cover 47 is an untreated, transparent outer dust coverand the adjustable transmission-loss layer 50 is adjusted to be fullytransparent, the user will view the surrounding environment at fullbrightness. However, in embodiments in which the outer dust cover 47 isa partial mirror, the surrounding environment will appear slightlydarker than it is in reality due to transmission-loss from the partialmirror preventing all of the light from the surrounding environment frompassing through the outer dust cover 47 to the user's eye. Oneadditional way to adjust the brightness of the projected visual content55 as seen by the user is to either brighten or dim the output oflight-emitting visual source 20.

In an alternate embodiment, the adjustable transmission-loss layer 50could simply be removed altogether and replaced with a set of darkenedfilters having a fixed level of transmission-loss, similar tosunglasses, that are attached to the exterior surface of the outer dustcover 49. These filters would allow only a fixed percentage of incidentlight to pass there through. In yet another alternate embodiment, theremay be no adjustable transmission-loss layer 50 at all and the outerdustcover 47 itself may be a substantially transparent set of darkenedfilters. In this embodiment, the brightness of both the projected visualcontent 55 and the surrounding environment in the mixed-reality view maybe determined primarily by the color and/or shade of the transparentmaterial from which the transparent outer dust cover 47 is made. If, forexample, the transparent outer dust cover were charcoal in color, thenthis would result in some transmission-loss of outside light passingthrough the outer dust cover 47. In this case the projected visualcontent would appear brighter while the view of the surroundingenvironment would appear darker than if the outer dust cover 47 were acolorless transparent material.

Furthermore, in any of the aforementioned embodiments in which the frontdust cover 46 and outer dust cover 47 are both transparent or allow auser to view the real-world surrounding environment, the secondaryvision housing 45 may be configured to allow a prescription lens (notshown) to be attached thereto for providing a user with prescriptionfocus correction if needed to clearly view the surrounding environmentthere through. In an alternate embodiment, the front dust cover 46 ofthe secondary vision housing 45 may be a permanent prescription lens,specific to the prescription focus correction needs of the user, forwhen the user is viewing the surrounding environment there through.

In yet another alternate embodiment, the outer dust cover 47 can be apermanent and substantially opaque shell preventing the user from seeingthe surrounding environment there through. In this manner the user canonly view the reflection of the projected visual content that isreflected off of the interior surface 48 of the outer dust cover 47,which is also the last reflective optical surface 36. Furthermore, inthis alternate embodiment, no corrective lens shape need be formed inthe exterior surface 49 of the outer dust cover 47, because it is notpossible to see through the outer dust cover 47.

Referring to FIG. 3A, as previously disclosed, the HMD device 5 includesa first 31 and a last 36 reflective optical surface, and in oneembodiment includes at least one intermediate reflective optical surface(not shown). In one embodiment, the HMD device 5 is a device that has atotal of five reflective optical surfaces, with the at least oneintermediate reflective optical surface 32 comprising a second 33, athird 34, and a fourth 35 reflective optical surface. In thisembodiment, the first 31 and third 34 reflective optical surfaces areconcave surfaces, the second 33 and fourth 35 reflective opticalsurfaces are convex surfaces, and each of the first 31, second 33, third34, and fourth 35 reflective optical surfaces are substantially fullymirrored surfaces located within the primary transmission housing 40.Furthermore, as previously disclosed in one embodiment, the lastreflective optical surface 36 is the concave transparent interiorsurface 48 of the outer dust cover 47, which is comprised of atransparent material, such as polycarbonate. However, the disclosure ofthe aforementioned five reflector HMD device should not be read to limitthe scope of HMD devices to only those HMD devices utilizing fivereflective optical surfaces. Accordingly, alternate embodiments mayexist that utilize fewer than, or more than, five reflective opticalsurfaces and that continue to fall within the scope of the presentdisclosure.

Referring to FIGS. 5 and 6, in an alternate embodiment, the HMD device 5may be a device that has a total of three reflective optical surfaces30, with the at least one intermediate reflective optical surface 32comprising a second 33 reflective optical surface. In this alternateembodiment, the first reflective optical surface 31 is a concavesurface, the second reflective optical surface 33 is a convex surface,and both of the first 31 and second 33 reflective optical surfaces aresubstantially fully mirrored surfaces located within the primarytransmission housing 40. Additionally, the last reflective opticalsurface 36 is the concave, transparent interior surface of the outerdust cover 47, which is comprised of a transparent material, such aspolycarbonate.

Determining the Geometry of the Reflective Optical Surfaces

In one embodiment, the geometric shapes of each of the reflectiveoptical surfaces are determined by utilizing a high end optical designsoftware, such as CODE-V written by Optical Research Associates, ZEMAXwritten by ZEMAX Development Corporation, or OSLO written by SinclairOptics, Inc. in order to define the shapes of the reflective opticalsurfaces based on a large list of independent design input variableschosen by, and having input values set by, a HMD system developer. Eachof these aforementioned example high end optical design softwarepackages should be familiar to one skilled in the art of optical systemdesign.

The shape of each mirror and the associated algorithms that define theshape of each mirror are output by the software and are determined basedon a significant number of input variables that are chosen by, and havetheir values set by, the system developer. These variables are specificdesign parameters that are chosen based on the desired overall system orthe specific design requirements. In one embodiment, the operator of thesoftware independently selects the design input variables and theirassociated values and input them into the optical design software priorto running a computer analysis that will output the geometric shapes andthe associated algorithms that define those shapes. Among the lengthylist of design variables whose values are to be determined and inputinto the software, prior to running any computer analysis, are thefollowing: the desired number of separate reflective optical surfacesand/or refractive elements in the overall primarily reflective-basedsystem; whether each reflective optical surface is to be concave,convex, flat, some unique alternate geometry, or a combination thereof;the desired range of eye-relief related to the last reflective opticalsurface; the desired dimensions of the eyebox; the desired FOV angle forthe overall reflective system; the amount of acceptable or desiredvisual content distortion, such as pincushion or barrel distortion, thatmay be observed by the HMD device user; the desired dimensions of theoverall system package (i.e., the package envelope); the desired exitingangle of vision; whether mixed-reality viewing is desired; the manner inwhich the projected light waves will enter the system from the visualsource 20 and the desired manner in which they should exit the systemfrom the last optical surface 36; and whether you want the overallsystem to be an above-eye, below-eye, or to the side of the eye system.This list is by no means an exhaustive list of variables and has beenprovided as an exemplification of possible system design choice inputvariables. Other design variables exist that will affect the output ofthe software analysis and any resulting mathematical algorithms thatdefine the shape of each reflective optical surface. The variables thatare input into the software depend on the desired overall system or thespecific design requirements of the HMD device.

The following descriptions are provided in order to further clarify anddefine the aforementioned design variables referenced above. The eyerelief is the distance from the pupil of the user's eye to the centerpoint of the last reflective optical surface. The eyebox is the virtualarea through which the near parallel light bundle coming from the lastreflective optical surface may enter the user's eye. The eye box isoften a circular area defined by a diameter that is at least as largeas, if not significantly larger than, the pupil of the user's eye. Forexample, if in an average lighting situation the typical user has apupil that is 2 millimeters in diameter, it may be desirable to choosean eyebox dimension that is 10 millimeters in diameter. This would allowthe user to move the pupil of his eye within the eyebox in an upward,downward, left, or right direction and not lose sight of the visualcontent that is reflected off of the last reflective optical surface andthat is passing through the larger 10 mm eyebox. The FOV, as discussedpreviously, refers to the swept angular extent (often a diagonal angle)to which a user can see observable content reflected from the lastreflective optical surface. The dimension of the overall system package,or the “package envelope,” refers to the outer dimensions of the overallHMD device, including all optics housings. Lastly, the exiting angle ofvision refers to, in a mixed-reality view, the overall allowable angleof vision in which the user can view the outside world through the HMDdevice while wearing the HMD device.

Once the variables are chosen and their desired values have beendetermined by the system designer, the designer then initiates theanalytical portion of the optical design software to run a computerdesign analysis in order to determine the overall geometric shape ofeach reflective optical surface and their associated locations relativeto each other and relative to the user's eye. When the analysis iscompleted, the software outputs a complex algorithm that defines theshape of each geometric surface. If even a single one of the significantnumber of input variables is changed or altered even slightly, thegeometric shape of each reflective optical surface, their relativepositions, and the resulting mathematical algorithms that define thegeometric surfaces will change completely. Accordingly, there is onlyone specific generic formula used to define the geometry of eachsurface, which is based on the specific values of the chosen set ofinput variables. Therefore, with so many options of input variables andcorresponding values of those variables, there are quite literally aninfinite number of possible reflective optical surface geometries andassociated algorithms to define those geometries, all based on thespecific combination of independent input variables that are chosen andtheir selected values.

Operation of the HMD Device

Referring to FIG. 1, in operation, one embodiment of the five-reflectorHMD device 5 works as follows. An HMD device user places the frame 10and the attached optics housings 15 of the HMD device 5 onto his head ashe would a pair of eyeglasses. The optics housings 15 are positionedsuch that the secondary vision housings 45 are located in front of theuser's eyes with the front dust cover 46 and the outer dust cover 47being located in the user's direct line of sight. The user first seesthrough the transparent front dust cover 46 and then through thetransparent outer dust cover 47 to view his surrounding environment. Ifthe user does not naturally have at least 20/20 vision, and generallyuses some type of prescription lens correction to achieve 20/20 vision,then a prescription lens may be attached to the secondary visionhousing's 45 front dust cover 46 between the user's eye and the frontdust cover 46.

Power is supplied to both the light-emitting visual source 20 as well asthe variable translucent layer 50 that is in communication with theouter dust cover 47. A visual input signal is sent to the source inputof the light-emitting visual source 20. The light-emitting visual source20 accepts the visual input signal and converts it into visual contentto be projected. Referring to FIGS. 3A and 7 for the five-reflector HMDdevice (see FIGS. 6 and 8 for the three-reflector HMD device), thevisual content displayed on the light-emitting visual source 20 isprojected there from to the concave, first reflective optical surface31. The concave, first reflective optical surface 31 then reflects theprojected visual content to the convex, second reflective opticalsurface 33. The convex, second reflective optical surface 33 thenreflects the projected visual content to the concave, third reflectiveoptical surface 34. The concave, third reflective optical surface 34then reflects the projected visual content to the convex, fourthreflective optical surface 35. Each of the first 31, second 33, third34, and fourth reflective optical surfaces 35 are substantially fullymirrored surfaces. The convex fourth reflective optical surface 35 thenreflects the projected visual content to the concave, last reflectiveoptical surface 36, which, in one embodiment, is also the interiorsurface 48 of the transparent outer dust cover 47. The interior surface48 of the transparent outer dust cover 47, and accordingly the lastreflective optical surface 36, may be a partial mirror as previouslydescribed. The concave last reflective optical surface 36 then reflectsthe projected visual content through the front dust cover 46, as well asthrough any prescription lens attached thereto, and into a user's eye,or more specifically, to a virtual eyebox, where the visual contentappears magnified and in focus.

However, the disclosure of the operation of this embodiment should notbe read to limit the order in which the projected visual content isreflected from each of the plurality of reflective optical surfaces 30.In other words, the order in which the visual content is reflected fromthe reflective surfaces is not limited to only reflections occurring ina sequentially numbered order, with each reflective surface only beingutilized for one reflection of the visual content.

For example, in a system that would otherwise utilize seven reflectiveoptical surfaces to achieve a specific desired magnification and FOVangle (i.e., the sequential order of reflection of the visual contentis: Reflector #1, Reflector #2, Reflector #3, Reflector #4, Reflector#5, Reflector #6, Reflector #7), the same magnification and FOV may beable to be achieved with only five reflective optical surfaces, byutilizing one of the five reflective optical surface to perform thereflections of what otherwise would be achieved with three separatereflective optical surfaces (i.e., the order of reflection of theprojected visual content could be: Reflector #1, Reflector #2, Reflector#3, Reflector #1, Reflector #4, Reflector #5, Reflector #1).

Continuing on with the disclosure of the operation of one embodiment, ifthe visual content projected to the user's eye is not immediately seenby the user as being bright enough or clear and in focus, there areseveral adjustments the user can make to the HMD device 5 to improve oroptimize the user's see-through vision and achieve a more balancedmixed-reality view. First, referring to FIGS. 9A to 9C, regarding thebrightness of the projected visual content, if the user feels that thevisual content is not bright enough, the user can make adjustments tothe variably-adjustable transmission-loss layer 50 to make the layer 50darker and more opaque, and in turn increase the transmission-loss ofoutside light passing there through to make the projection of the visualcontent appear brighter. However, doing so also decreases the amount oflight entering the user's eye from the surrounding environment and thusdarkens the user's view of the real-world surrounding environment thatis seen through the projected visual content in the mixed-reality view.Conversely, if the user's view of the surrounding environment is toodark to be seen, or if it is simply not at the user's desired brightnesslevel, then the user may adjust the adjustable transmission-loss layer50 to make the layer 50 appear lighter and more transparent. This willdecrease the transmission-loss of outside light passing there throughand allow more light from the surrounding environment to pass throughthe layer 50 to reach the user's eye. This however, has the effect ofmaking the projected visual content appear lighter or less vivid to theuser in the mixed-reality view.

Second, referring to FIG. 4, regarding the clarity of the projectedvisual content seen by the user, if the projected visual content is notclearly in focus, the user may make manual adjustments to the diopteradjuster 25 so as to move the light-emitting visual source 20 closer toor further away from the first reflective optical surface 31 locatedinside the primary transmission housing 40. This results in acorresponding adjustment to the position of the final focal point of theprojected visual content within the user's eye, or within the eyebox,thus allowing the user to clearly focus the visual content.

One of the major benefits associated with a primarily reflective-basedHMD device 5, as presently disclosed herein, is that because there is noneed for any heavy glass or acrylic refractive lenses and mountinghardware within the device in order to achieve magnification and focusof the projected visual content, the HMD device 5 is extremelylightweight and comfortable for the user to wear, more so than any otheravailable HMD device. Furthermore, because the reflective-optics do notrequire separate and expensive refractive lenses, the manufacturing costassociated with the HMD device disclosed herein are significantly lessthan other HMD devices currently available in the consumer, commercial,or military markets. This also translates to a significantly lowerpurchase price for the final HMD device 5. In addition, the primarilyreflective-based HMD device 5 as disclosed herein is capable ofachieving large text-readable FOV angles and increasing the FOV anglefrom one embodiment of the device to another embodiment of the devicewithout adding significant cost or weight to the HMD device 5. Lastly,another benefit associated with the HMD device disclosed herein is thatbecause the optics housings 15 of the primarily reflective-based HMDdevice 5 are extremely compact, the HMD device 5 is a near-to-eyedevice.

General Physical Description of an Embodiment of a HMD

A HMD according to one embodiment is an article to be worn by a user andprovides a stereo view of an electronically generated image. The imageis generally processor generated or computer generated, and may be astill image or a moving animation image. The image may includephotographical, graphical, text, or other types of visual subjectmatter. In some use cases, the image as seen by the user may be shieldedfrom outside light so as to provide the user with a completely immersiveexperience. In some use cases the image as seen by the user may providethe user with an “augmented” view of reality; that is, the image may besuperimposed upon an outside view of the real world around the user.

An assembled view of an advantageous embodiment of a HMD 102 is depictedin FIGS. 10-13. FIG. 10 generally depicts an isometric frontal view ofthe HMD 102. FIG. 11 depicts a rear view according to the perspective ofa user looking through the HMD 102. FIG. 12 depicts a top view and FIG.13 depicts a side view of HMD 102.

Directional axes X, Y, and Z are defined in FIGS. 10-13. Generally theX-axis is defined as horizontally left to right according to a userwearing the HMD 102. The X-axis generally follows a top portion 104 ofan outer frame 106 of the HMD 102. Construction of the HMD 102 includingframe 106 is described in further detail below. The Y-axis is defined asa vertical axis that is approximately aligned with a gravitationalreference when the HMD 102 is in use and a user is standing or sittingup. Finally the Z-axis is defined as being approximately aligned withthe “line of site” of the user of the HMD 102 when the user is lookingforwardly through the HMD 102 in a forward direction. Axes X, Y, and Zare generally mutually orthogonal.

In terms of directions, we refer to left and right along the X-axis ascorresponding to the left and right eyes of the user. Upward anddownward, with respect to the Y-axis, refers to a gravitational frame ofreference when a user is standing erect and wearing HMD 102. Forwardwith respect to the Z-axis refers to the user's line of sight and awayfrom the user. Rearward with respect to the Z-axis is opposite to theforward direction with respect to Z-axis and toward the user.

Other features depicted in FIGS. 10-13 are two micro-display mechanisms108 positioned along and below the top portion 104 of outer frame 106.The X-position of each micro-display mechanism 108 is approximately thesame as the X-position of each of the user's eyes. Each micro-displaymechanism 108 contains a small micro-display mounted in a positioningmechanism for adjusting a position of the micro-display along the X andZ-axes. The positioning mechanism includes an X-axis position adjuster110 for moving the micro-display along the X-axis, and a Z-axis positionadjuster 112 for moving the micro-display along the Z-axis. Themicro-display mechanism 108, including component parts, action, andassembly, will be discussed in more detail below.

Optical Path

The optical path of HMD 102 according to one embodiment is principallydefined by a micro-display and a series of non-rotationally symmetrical,free-form reflective optics. This means that the optical elements arenot rotationally symmetric about an axis that is generally along anoptical ray path that passes through the focal point of the light raybundle. Essentially, the optical elements are non-spherical elements(asphere free forms). The micro-display is very compact, typicallyranging from 0.37″ (on the diagonal) to 0.97″ (on the diagonal). Themirrors, or reflectors or reflective optical surfaces, are generallyarranged to reflect light back and forth with respect to an axis, whichaxis is generally in line with the user's line of sight (e.g., Z-axis).In an exemplary embodiment this technique uses only air as the lighttransmission medium. Most HMD optical systems utilize a higherrefractive index material for their light path. This introduces moreweight and cost than using air. Each of the reflectors (e.g., threereflectors in one embodiment) are generally elongated, with a major axislying along a horizontal axis (e.g., X-axis), and a minor axis lyingalong a vertical axis (e.g., Y-axis). Each of the reflecting mirrors isfreeform, or asymmetrical, with respect to the horizontal X-axis, whilebeing symmetrical with respect to the vertical Y-axis. The reflectorsare each either concave or convex. In an exemplary embodiment, HMD 102includes three reflective or mirrored surfaces referred to as M1, M2,and M3 in the respective order of light being reflected from themicro-display. In the exemplary embodiment, M1 is concave, M2 is convex,and M3 is concave.

In the exemplary embodiment: (1) the micro-display faces generallyforward or away from the user with respect to the user's line of sight;(2) the M1 mirror is positioned just below the micro-display withrespect to the vertical Y-axis, and has its reflective surface facinggenerally backwards and toward the user; (3) the M2 mirror is positionedjust below the M1 mirror with respect to the vertical Y-axis and has itsreflective surface facing generally forward and away from the user; (4)the M3 mirror is positioned just below the M2 mirror with respect to thevertical Y-axis and has its reflective surface facing generallybackwards and toward the user.

The optical path passes light and images from the micro-display in aback and forth manner, relative to the user's line of site along theZ-axis, and vertically downward, relative to a gravitational referenceand the Y-axis, reflecting the light ray bundle off of each successivemirror, until it reaches the user's eye. The optical path is (1) fromthe micro-display to M1, (2) from M1 to M2, (3) from M2 to M3, and (4)from M3 to the user's eye.

This method of creating a magnified image incorporates a non-pupilforming system, providing a tele-centric optic path into the pupil. Inother words, the light rays entering the user's eye in the presentlydisclosed system are parallel so that the image is always visible,regardless of the position of a user's pupil. A rather large exit pupilis formed, on the order of 8 mm. These aspects of the HMD 102 affordmaximum eye comfort and ease of viewing, with no vignetting. In otherwords, there is no reduction in the image's brightness or saturation atthe periphery compared with the image center. This size of field ofview, in this small form-factor has not been possible prior to thisoptical solution.

Illustrations of an optical path 114 defined by optical components ofHMD 102 are depicted in FIGS. 14 and 15. The optical path 114 isdepicted as being purely reflective between a micro-display 116 and auser's eye 118. Between the micro-display 116 and the user's eye 118 area series of freeform reflective optics or mirrors. The mirrors arereferred to as freeform because they are asymmetrical; that is they arenot symmetrical with respect to a central ray path. They are symmetricalwith respect to the vertical Y-axis in the exemplary embodiment depictedwith respect to FIGS. 14 and 15.

The optical path 114 begins with a rectangular micro-display 116, whichis generally a relatively small panel that emits an image. In oneembodiment, the micro-display 116 has a diagonal length of between 0.2inch to 1.0 inch. For an example consumer device, the diagonal length ispreferably in the range of 0.3 inch to 0.6 inch. In one embodiment, theconsumer version of the micro-display diagonal length is about 0.37inch. For a military embodiment, the diagonal length is about 0.97 inch.

Examples of image emitting technology for micro-displays 116 includeOLED (organic light emitting diode) displays, LCOS (liquid crystal onSilicon) displays, or LCD (liquid crystal display). Referring to FIG.14, the image from the micro-display 116 passes along a first opticalpath segment 120 to an M1 mirror 122. The first optical path segment 120includes light rays that generally diverge between the micro-display 116and the M1 mirror 122. The rays of the first optical path segment 120are on average nearly parallel with the Z-axis, but define an acuteangle with respect to the Z-axis. The first optical path segment 120 isgenerally directed forward from the micro display 116 along the Z-axis,and downward along the Y-axis.

The first mirror, M1 122, has an elongated geometry having a major axisdisposed along the X-axis and a minor axis disposed along the Y-axis.However, M1 mirror is not planar; rather, it is concave, but its extentgenerally lies along the X and Y-axes with a small Z-axis component.

The second optical path segment 124 extends between M1 mirror 122 and M2mirror 126. The second optical path segment 124 is generally directedrearward from M1 mirror 122 with respect to the Z-axis, and downwardwith respect to the Y-axis. Because M1 mirror 122 is concave, the raysalong second optical path segment 124 generally converge.

M2 Mirror 126 is generally convex and has an elongated geometry having amajor axis disposed along the X-axis and a minor axis disposed along theY-axis. The third optical path segment 128 extends between mirror M2 126and mirror M3 130. The third optical path segment 128 is generallydirected forward from M2 mirror 126 along the Z-axis, and downward alongthe Y-axis. Because the M2 mirror 126 is convex, the rays along thethird optical path segment 128 generally diverge.

M3 Mirror 130 is concave and is generally disposed along the X andY-axes. The fourth optical path segment 132 extends between the M3mirror 130 and the user's eye 118. The fourth optical path segment 132is generally directed rearward from the M3 mirror 130 along the Z-axis,and downward along the Y-axis. Because the M3 mirror 130 is concave, therays along fourth optical path segment 132 generally converge toward theuser's eye 118.

The mirrors M1 122, M2 126, and M3 130 are generally disposed primarilyalong the X and Y-axes. However they may also may have a general tiltwith respect with the X-axis in order to define the entire optical path114. Therefore, to a minor extent, the mirrors lay along the Z-axis aswell. Also they are non-planar, and so this description is approximate.

As can be seen, the entire optical path 114, including the first 120,second 124, third 128, and fourth 132 optical path segments, isprogressively, or monotonically, directed downward with respect to theY-axis, while being directed in alternating forward and rearwarddirections, with respect to the Z-axis, as the light rays travel thepath 114 from the micro-display 116 to the user's eye 118. The opticalpath 114 is alternately divergent and convergent between themicro-display 116 and the user's eye 118. One interesting aspect of thisoptical path is that it has no stops. That is to say there is no pointthat the ray bundle converges to a point and flips over. Most opticsystems use stops in their optic path. The optical path of HMD 102according to one embodiment utilizes the user's pupil as the stop of thesystem. This direct-path optical magnifier produces a non-pupil forming,tele-centric exit pupil ray bundle. This type of optic system produces anatural, relaxed viewing experience.

The optical path depicted in FIGS. 14 and 15 can provide a large fieldof view (FOV). The FOV can be described in terms of full overlap,partial overlap, or zero overlap. Full overlap is when the right andleft images are fully superposed on each other such that they addressthe same field of view. Zero overlap is when the right and left imagescover different fields of view. Partial overlap is when there is acentral portion of the image that has an overlapping field of view withportions unique to the left and right eyes.

The optical path described with respect to FIGS. 14 and 15 enables afull overlap FOV to be more than 40 degrees, more than 50 degrees, up to60 degrees or more than 60 degrees. The optical path described withrespect to FIGS. 14 and 15 enables a zero overlap FOV to be more than 80degrees, more than 100 degrees, up to 120 degree, or more than 120degrees. Partial FOV values enabled would be an interpolation of thefull overlap FOV and the zero overlap FOV.

Structural Support of Optical Components

Some embodiments utilize a separate optical supporting sub-chassis whichresides inside a separate outer non-optically supporting eyeglass frame.The mechanical support for the optical path includes a structural framethat provides multiple functions including supporting all opticalcomponents and providing a form factor that is configurable into a lightweight set of eye glasses. The structural frame is made of a materialthat has a low coefficient of thermal expansion and a high elasticmodulus. In an exemplary embodiment the sub-chassis is formed of amolded or cast magnesium alloy. In a further exemplary embodiment thealloy is AM60B which is a magnesium alloy composition containingprimarily Magnesium but also Aluminum, Manganese, Zinc, and othermetals. The ultimate tensile strength of AM60B is 220 MPa. The tensileyield strength of AM60B is 130 MPa. The density of resultant castmaterial is 1.79 grams per cubic centimeter.

The structural frame including attached optical components isconstructed in such a manner as to provide accurate critical datums forreceiving the optical elements and facilitating assembly. The structuralframe has an upper rim and a lower rim relative to the vertical Y-axiswith two openings defined there between, with datums. Formed into theupper rim are two pockets that are roughly aligned with the user's eyesin a horizontal X-axis, which contain additional datums. Each pocket isconfigured to receive a micro-display mechanism which supports amicro-display, which micro-display mechanism contains its own alignmenttabs, which rest in the structural frame datums. Upon installation intoa pocket, each micro-display mechanism extends downwardly from the upperrim toward the lower rim. In an exemplary embodiment each pocket extendsless than half of the distance from the upper rim toward the lower rim.In an exemplary embodiment each micro-display faces forward relative toa line of site of the user, which is to say away from the user's eye. Inan exemplary embodiment each micro-display mechanism provides amechanism for the user to adjust a focal and lateral position of eachmicro-display.

At a lower or distal end of the pocket is a mount for an optical elementwhich, in one embodiment, is referred to as M2 mirror 126. The M2 mirror126 is a convex mirror that faces forward relative to the line of siteof the user.

Each of the two openings in the structural frame is configured toreceive a compound optical element. The compound optical element isformed of an optically clear, low specific gravity, high tolerance anddimensionally stable material. In an exemplary embodiment the clearmaterial is a polymer from the cyclo olefin polymer (COP) family.

An example material used for the compound optical element and the M2mirror 126 are ZEONEX F52R. Features to the material are: extremely lowbirefringence and excellent stability under severe conditions (hightemperature and high humidity). The refractive index is 1.535. TheBirefringence ratio is 0.5. The glass transition temperature is 156 deg.C.

Each compound optical element defines two optical elements including anM1 reflective optical surface, or mirror 122, and an M3 reflectiveoptical surface, or mirror 130, that are both concave mirrors that facerearward, relative to the user's line of sight, which is to say backtoward the user's eyes. These compound optical elements incorporatetheir own alignment tabs, which correlate to the datums in the opticalstructural frame, which facilitate optical alignment during assembly.

Thus a single structural frame rigidly supports two micro-displayassemblies (one for each of the user's two eyes), two compound opticalelements, and two concave mirrors that collectively define an opticalpath for each eye. The optical path for each eye starts at amicro-display and then traverses (1) forward to an M1 mirror, (2)rearward from the M1 mirror to an M2 mirror, (3) forward from the M2mirror to an M3 mirror, and (4) backward from the M3 mirror to the eye.

The structural frame therefore functions as both a major structuralportion of a pair of glasses and at the same time holds a series ofoptics in precision alignment. This method provides ease of assembly andvery accurate alignment of the optical elements and micro-displayholder/mechanism. Unlike prior glasses frames this structural frame hasa very high modulus and is dimensionally stable enough to provideprecision optical alignments suitable for the optical path of an HMD.The unique geometric arrangement of these features enable a very lowprofile and compact optical path while enabling the user to adjust forfocus and interpupillary distance.

FIGS. 16 and 17 depict structural features of the HMD 102 that definethe optical path 114. FIG. 16 is a rear perspective view of a structuralframe 134 that is essentially the mechanical backbone of the opticalpath 114. Embodiments maintain accurate and stable alignment of themirrors 122, 126, 130 and the micro-display 116 because small errors inorientation or alignment of optical components will adversely affect theimage seen by the user. An aspect of the optical structure is thestructural frame 134. The structural frame 134 should have a very goodstrength but at the same time be extremely lightweight.

Thus, one attribute is the specific gravity of the structural frame 134.In one embodiment the specific gravity of the structural frame materialis less than 3. In another embodiment the specific gravity is less than2. In an exemplary embodiment the specific gravity is in the range of1.5 to 2.0. The relatively low specific gravity of the material isemployed for user comfort because any excess weight in eyeglasses isnoticeably uncomfortable.

In an exemplary embodiment the structural frame 134 is formed from aninjection molded or cast magnesium alloy. This enables a lightweight andhigh performance frame to be formed with a very efficient and low costprocess. Typical magnesium alloys can include, in additional to Mg,certain amounts of aluminum, manganese, silicon, copper, zinc, iron andnickel to name a few other elements. Examples of such alloys includematerials known by the following alloy names: AM60A, AM60B, AZ71E,AZ91A, AZ91B, AZ91C, AZ91D, AND AZ91E to name a few examples.

The AM60A and AM60B alloys have a tensile strength of about 220 MPa(million Pascal) or about 32 KSI (thousand pounds per square inch). Theyield strength is about 130 MPa. The elastic modulus in tension is about45 GPa (Giga Pascal) or about 6.5 million PSI (pounds per square inch).What is outstanding about these materials is the low specific gravity ofabout 1.8 (1.8 grams per cubic centimeter measured at 20 degreesCelsius). Thus these alloys provide an exceptionally lightweight andstrong material for the structural frame 134. The other cast magnesiumalloys listed above have similar properties.

The structural frame 134 includes an upper rim 136 and a lower rim 138with openings 140 defined there between. The upper rim 136 defines anupper portion of the structural frame 134 with respect to the Y-axis.The lower rim 138 defines a lower portion of the structural frame 134with respect to the Y-axis.

Referring to FIG. 16, two pockets 142 extending downwardly with respectto the Y-axis are defined in a portion of upper rim 136. Each pocket 142is configured to receive a micro-display mechanism 108. At a lower ordistal extent of each pocket 142 with respect to the Y-axis is a mount144 configured to support an M2 mirror 126.

Openings 140 in structural frame 134 are each configured to receive andsupport a compound optical element 146.

As shown in FIG. 17, compound optical elements 146 are primarilydisposed along the X and Y-axes although they both have a concavegeometry with respect to the optical path 114. Each of compound opticalelements 146 are “compound” in the sense that they each have twodifferent optical elements, including an M1 mirror 122 and an M3 mirror130. In an exemplary embodiment, compound optical elements 146 areformed of an optically clear, light weight and highly dimensionallystable polymer from the cyclo olefin polymer (COP) family.

An example material used for the compound optical element 146 and the M2mirror are ZEONEX F52R. Features to the material are: extremely lowbirefringence and excellent stability under severe conditions (hightemperature and high humidity). The refractive index is 1.535. TheBirefringence ratio is 0.5. The glass transition temperature is 156degrees Celsius.

The M1 mirror 122 and the M2 mirror 126 are both opaque and as close to100% reflective as possible in order to maximize optical efficiency ofthe light path 114. On the other hand, the M3 mirror 130 is partiallyreflective and allows external light from outside compound opticalelement 146 to pass there through and reach the user's eye. Anelectrochromic covering is used in conjunction with compound opticalelement 146 to allow a user to vary the amount of environmental lightthat may reach compound optical element 146.

In an exemplary embodiment the clear material of the compound opticalelement 146 has a zero optical power to allow a user to have a neutral,undistorted forward vision to the “outside world.” The frequencyresponse of all mirrored surfaces are as flat as possible in the 400 nmto 800 nm visible optical band.

In an alternative embodiment the M1 and M3 mirrors can be formed fromtwo different optical elements. This would enable decoupling themanufacture of the two optical elements but would add some complexity tothe overall assembly. The functions and properties of the separateoptical elements would be essentially the same as their integratedcounterparts.

As can be seen, the structural frame 134 performs a number of functionsincluding supporting and holding all optical components of optical path114 in alignment including the micro-displays 116, the compound opticalelements 146, and the M2 mirrors 126. The assembly of the structuralframe 134 and the optical components provides a rigid, accurate, anddimensionally stable optical path 114 while being very lightweight andcomfortable for a user. This optical assembly as described with respectto FIGS. 16 and 17 enables the field of view (FOV) values described withrespect with FIGS. 14 and 15 while being very compact and lightweight.

Micro-Display Mechanism

A compact and accurate optical path alignment mechanism is provided forHMD 102. The optical path includes a micro-display and at least oneoptical element that transmits an image from the micro-display to theuser's eye. The alignment mechanism is configured to accommodate theuser's pupil location along two axes: (1) a Z-axis that is generallyalong the user's line of site, which corresponds to a focal length ofthe optical path; and (2) an X-axis that is horizontal and transverse tothe line of site, which corresponds to a interpupillary distance (IPD)for the user. The alignment mechanism provides this accommodation bydiscretely moving the micro-display along these two axes.

This mechanical method of varying the IPD allows the entire opticalassembly to remain stationary in the eyeglass frame while providing atwo-axis adjustment; front-to-back for focal length adjustment, and leftto right for IPD adjustment. The micro-display holding mechanism movesthe display laterally (left or right) relative to the M1 mirror. Due tothe geometry of the M1 mirror, being primarily a bi-concave reflector,when the centerline of the display is shifted left or right on thehorizontal plane, as the light rays from the display enter the M1off-center, the output ray bundle is shifted left or right, causing thedistance from the ray bundle to the centerline of the display to change.

In an exemplary embodiment, the entire micro-display mechanism fits intoan envelope of less than 30 mm in X direction (left to right), less than15 mm in the Z direction (along the line of sight of the user) and lessthan 20 mm in the Y direction (perpendicular to X and Z). In a furtherexemplary embodiment the envelope size of the display mechanism assemblyis: 29 mm in X, 13.85 mm in Z, and 18 mm in Y.

FIGS. 18A-F depict various views of micro-display mechanism 108. FIGS.18A and 18B depict micro-display mechanism 108 in exploded form toillustrate various elements of and an assembly process for micro-displaymechanism 108. Micro-display mechanism 108 includes carriage 148,micro-display holder 150, X-gear 152, and Z-gear 154. Carriage 148defines slots 155 for constraining motion of the micro-display holder150, opening 157 for receiving a shaft 166 of X-gear 152 and openings159 for receiving shaft 172 of Z-gear 154.

Micro-display holder 150 includes upper portion 156 and lower portion158. Lower portion 158 extends downwardly with respect to axis Y fromcarriage 148 and supports micro-display 116. Upper portion 156 includesupwardly extending teeth 160 and downwardly extending teeth 162.Micro-display holder 150 also includes outwardly extending tabs 161 tobe received into slots 155 of carriage 148.

X-gear 152 includes a user-manipulation portion 164 attached to shaft166. Shaft 166 includes radially extending teeth 168 for engagement withupwardly extending teeth 160 of micro-display holder 150. Z-gear 154includes a user-manipulation portion 170 attached to shaft 172. Shaft172 includes radially extending teeth 174 for engagement with downwardlyextending teeth 162 of micro-display holder 150.

FIGS. 18A-B depict the assembly of micro-display mechanism 108. At theillustrated stage of assembly micro-display 116 is already attached tolower portion 158 of micro-display holder 150. The remaining stepsinclude:

(1) The upper portion 156 of micro-display holder 150 is assembled tocarriage 148. This step includes tabs 161 being received into slots 155along the Z-axis. Once tabs 161 are fully received into slots 155, themotion of micro-display holder 150 (and hence micro-display 116) withrespect to carriage 148 is constrained to user-manipulated motion alongthe X-axis and Z-axis while rotational motion is restrained.

(2) The Z-gear shaft 172 is inserted into openings 159 of carriage 148along the X-axis. As a result of this insertion the radially extendingteeth 174 of shaft 172 engage downwardly extending teeth 162 ofmicro-display holder 150.

(3) The X-gear shaft 166 is inserted into opening 157 of carriage 148along the Z-axis. As a result of this insertion the radially extendingteeth 168 of shaft 166 engage upwardly extending teeth 160 ofmicro-display holder 150. This engagement forms a rack and pinion actionbetween X-gear 152 and the upper portion 156 of micro-display holder150.

FIG. 18C depicts micro-display mechanism 108 in fully assembled formalong with X and Z axes. Twisting the user manipulation portion 164 ofthe X-gear 152 (FIG. 18B) moves the display 116 along the X-axis toadjust inter-pupil distance (IPD). Manipulating the user manipulationportion 170 of the Z-gear 154 (FIG. 18B) moves the display 116 alongZ-axis to adjust the focal point of the optical path 114.

The entire micro-display mechanism 108 fits into an envelope of lessthan 40 mm (millimeters) in X (left to right), less than 20 mm in Z(along the line of sight of the user) and less than 30 mm in Y(perpendicular to X and Z). In one embodiment the micro-display fitsinto an envelope of less than 35 mm in X, less than 15 mm in Z, and lessthan 20 mm in Y. In a further exemplary embodiment the envelope size ofthe micro-display mechanism is: 29 mm in X, 13.9 mm in Z, and 18 mm inY. Reducing the size is particularly beneficial for users who areconsumers who will find a bulky head mounted display to beobjectionable.

FIG. 18D is a back view of micro-display mechanism 108 illustrating theaction of X-gear 152. The upper portion 156 of micro-display holder 150and the shaft 166 of X-gear 152 form a rack and pinion action. This rackand pinion action includes the engagement of radially extending teeth168 of shaft 166 and upwardly extending teeth 160 of upper portion 156.This engagement allows rotational motion of shaft 166 to induce linearmotion of upper portion 156 in X. This rack and pinion arrangementallows twisting of user manipulation portion 164 to translatemicro-display 116 back and forth along the X-axis to line up a lightbeam originating from micro-display 116 with a user's pupil in theX-direction. This adjustment applied to both left and rightmicro-display mechanisms thereby adjusts the IPD (inter-pupil distance).

FIG. 18E depicts an engagement between the tabs 161 of micro-displayholder 150 and slots 155 of carriage 148 which constrains the motion ofmicro-display holder 150. The constraint is to linear motion along X andZ. The engagement constrains motion of micro-display holder 150 to the Zaxis in response to manipulation of portion 170 of Z-gear 154.

FIG. 18F depicts the action of Z-gear 154 upon micro-display holder 150.Manipulation of portion 170 (FIG. 18E) causes rotation of shaft 172 ofZ-gear 154. Radially extending teeth 174 of Z-gear 54 engage downwardlyextending teeth 162 of micro-display holder 150 so that rotation ofshaft 172 translates micro-display holder 150 along the Z axis. Motionof micro-display holder along Z adjusts the focal point of light raysreaching the user's eye from micro-display 116.

HMD Assembly Process

An efficient design and manufacturing process provides a very compact,dimensionally accurate, dimensionally stable, and impact resistant HMD.The design includes a rigid and high modulus structural frame thatsecures and provides a stable support and alignment for opticalcomponents. A relatively lower modulus polymer outer frame is assembledto the rigid inner frame. The outer frame provides a dust cover forcomponents mounted to the structural frame along with temple arms forsecuring the HMD to a user's head. The outer frame also provides acomposite structure that withstands impact by virtue of the combinationof the relatively lower modulus outer frame in combination with thehigher modulus inner frame.

The optical components include a micro-display and at least onereflective optical element that are rigidly secured to the structuralframe. An optical path is defined between the micro-display, the atleast one optical element, and a user's eye. The micro-display and theat least one reflective optical element are rigidly secured to thestructural frame before the structural frame is received into andassembled to the outer frame.

In an exemplary embodiment the optical elements include (1) a pair ofcompound lenses that each provide two of the reflective optical elementsthat form a portion of the light path and (2) a second mirror element.These lenses are directly secured to the structural frame via theiralignment tabs and mating datums on the structural frame. The compoundlenses and the mirror element may be secured to the structural frameusing an adhesive.

In an exemplary embodiment the micro-display is integrated into amicro-display mechanism that allows for user adjustment of theinterpupillary distance and focus. The micro-display mechanism isassembled to the structural frame by securing the micro-displaymechanism into a mechanical pocket that is formed into the structuralframe. The micro-display mechanism has alignment tabs integrated intoits structure, which rest in mating datums in the structural frame.

This design allows for a very efficient assembly of the HMD. The designresults in a lightweight, compact, precise, dimensionally stable, andimpact resistant HMD that has not been achieved in any prior designs.

An overall assembly process for the HMD 102 is depicted in FIG. 19.According to 176 the outer frame 106 is assembled. FIG. 20 depictsfurther details of the outer frame assembly. According to 178 themicro-display mechanism 108 is assembled as discussed with respect toFIGS. 18A and 18B. According to 180 the optical components are assembledto the structural frame for which there is further detail in FIG. 21.According to 182 final assembly of HMD 102 takes place as is depicted inFIG. 22.

Steps 176 and 178 do not need to be done in any particular order.However, step 178 needs to be performed before step 180 and step 180needs to be performed before step 182.

Step 176 of FIG. 19 is depicted in additional detail according to FIG.20 which illustrates an exemplary embodiment of a process for assemblingouter frame 106. This exemplary process includes the following steps:

(1) Electro-transmissive lenses 184 are attached to frame 106. Lenses184 function as both a dust covering and as a way of modulating lightthat may enter the HMD 102. In one embodiment the lenses are secured byan adhesive.

(2) Rubber tips 185 are attached to temple arms 186. (3) Temple arms 186are attached to outer frame 106.

An exemplary embodiment of step 178 has already been described withrespect to FIGS. 18A and 18B. Step 180 of FIG. 19 is depicted accordingto FIG. 21 which is an exemplary process for assembling opticalcomponents to structural frame 134. The illustrated process involves thefollowing steps:

(1) Left and right M2 mirrors 126 are attached to mounts 144. In anexemplary embodiment the mirrors are attached with an adhesive.

(2) Left and right compound lenses 146 are attached to frame 134. Afterattachment, the compound lenses 146 each cover a portion of one opening140. In an exemplary embodiment the lenses 146 are secured to the frame134 using an adhesive.

(3) Left and right micro-display mechanisms are lowered along the Y-axisinto left and right pockets 142 respectively. After assembly an uppersurface of carriage 148 (FIG. 18 A) is exposed above each pocket 142 andthe lower portion 158 (FIG. 18B) of each micro display mechanism 108extends downwardly into pocket 142.

Step 182 of FIG. 19 is depicted according to FIG. 22 which is anexemplary final assembly process for HMD 102. The illustrated processhas the following steps:

(1) The now-assembled structural frame 134, as assembled according toFIG. 21, is received into the outer frame 106. According to FIG. 22structural frame 134 is received into outer frame 106 along the Z-axis.In an exemplary embodiment the structural frame is secured to the outerframe 106 using an adhesive.

(2) A dust cover 188 is secured to a rearward side of the outer frame106. In an exemplary embodiment the dust cover 188 is secured to theouter frame 106 using an adhesive. Because compound lens 146 (FIG. 21)does not completely cover openings 140, the front and rear dust covers(not shown) and 188 respectively are employed for protecting the opticalpath 114 components from dust and other contamination.

(3) Nose bridge 190 is attached to outer frame 106. (4) Nose insert 192is attached to nose bridge 190. Nose bridge 190 and nose insert 192enable HMD 102 to be customized to a wide range of user nose geometries.

FIG. 23 is a first bottom view of a structural frame showing tabs fromthe optical elements positioned within the notched datum positioningmounts of the structural frame according to one embodiment.

FIG. 24 is a second bottom view of a structural frame showing tabs fromthe optical elements positioned within the notched datum positioningmounts of the structural frame according to one embodiment.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to embodiments of the invention without departing from thescope of the disclosure and claims.

What is claimed is:
 1. A head mounted display device comprising: astructural frame arranged generally along a X-axis and a Y-axis forviewing along a Z-axis, the X, Y, and Z axes being mutuallyperpendicular; a micro-display coupled to the structural frame, andconfigured to project visual content in a substantially forwarddirection along the Z-axis away from a user, a group of one or moreoptical elements with reflective optical surfaces coupled to thestructural frame and respectively positioned on a front side of themicro-display to reflectively guide a light ray bundle from themicro-display to a user's eye; and a micro-display alignment mechanismmounted to the structural frame and configured to align and control thereflectively guided light ray bundle from the micro-display to theuser's eye by positioning the micro-display along the X and Z axes, themicro-display alignment mechanism comprising: a micro-display holderconfigured to hold the micro-display; and a carriage configured tocouple to and constrain motion of the micro-display holder to motionalong the X and Z axes and restraining rotational motion of themicro-display holder about the X and Z axes, wherein the micro-displayalignment mechanism fits into an envelope having dimensions of less than40 mm in X, less than 30 mm in Y, and less than 20 mm in Z.
 2. The headmounted display device of claim 1, wherein the micro-display alignmentmechanism is configured to adjust interpupillary distance by linearlydisplacing the micro-display along the X-axis while constraining againstrotational motion about the X-axis and the Z-axis.
 3. The head mounteddisplay device of claim 1, wherein the micro-display alignment mechanismis configured to adjust a focal point in a Z dimension of thereflectively guided light ray bundle by linearly adjusting the positionof the micro-display along the Z-axis while constraining againstrotational motion about the X-axis and the Z-axis.
 4. The head mounteddisplay device of claim 1, wherein the micro-display alignment mechanismfits into an envelope having dimensions of less than 35 mm in X, lessthan 20 mm in Y, and less than 15 mm in Z.
 5. The head mounted displaydevice of claim 1, wherein the micro-display alignment mechanism fitsinto an envelope having dimensions of less than 30 mm in X, less than 19mm in Y, and less than 14 mm in Z.
 6. The head mounted display device ofclaim 1, wherein the carriage is configured to constrainuser-manipulated motion of the micro-display holder to motion along theX and Z axes.
 7. The head mounted display device of claim 1, wherein themicro-display alignment mechanism comprises: a X-gear including auser-manipulation portion attached to a shaft configured to be receivedin a first opening in the carriage; and a Z-gear including auser-manipulation portion attached to a shaft configured to be receivedin a second opening in the carriage.
 8. The head mounted display deviceof claim 7, wherein: the micro-display holder includes upwardlyextending teeth; and the X-gear shaft is configured to insert into thefirst opening of the carriage along the Z-axis and includes radiallyextending teeth to engage the upwardly extending teeth of themicro-display holder.
 9. The head mounted display device of claim 8,wherein engagement of the radially extending teeth of the X-gear shaftto the upwardly extending teeth of the micro-display holder translatesrotational motion of the X-gear shaft to linear motion of themicro-display along the X-axis.
 10. The head mounted display device ofclaim 7, wherein: the micro-display holder includes downwardly extendingteeth; and the Z-gear shaft is configured to insert into the secondopening of the carriage along the X-axis and includes radially extendingteeth to engage the downwardly extending teeth of the micro-displayholder.
 11. The head mounted display device of claim 10, whereinengagement of the radially extending teeth of the Z-gear shaft to thedownwardly extending teeth of the micro-display holder translatesrotational motion of the Z-gear shaft to linear motion of themicro-display along the Z-axis.
 12. A head mounted display devicecomprising: a structural frame arranged generally along a X-axis and aY-axis for viewing along a Z-axis, the X, Y, and Z axes being mutuallyperpendicular; a micro-display coupled to the structural frame, andconfigured to project visual content in a substantially forwarddirection along the Z-axis away from a user; a group of one or moreoptical elements with reflective optical surfaces coupled to thestructural frame and respectively positioned on a front side of themicro-display to reflectively guide a light ray bundle from themicro-display to a user's eye, wherein the group of optical elementscomprise: a first mirror with reflective optical surface facing in asubstantially rearward direction along the Z-axis; a second mirror witha reflective optical surface facing in a substantially forward directionalong the Z-axis; and a third mirror with reflective optical surfacefacing in a substantially rearward direction along the Z-axis; and amicro-display alignment mechanism mounted to the structural frame andconfigured to align and control the reflectively guided light ray bundlefrom the micro-display to the user's eye by positioning themicro-display along the X and Z axes, wherein the micro-displayalignment mechanism fits into an envelope having dimensions of less than40 mm in X, less than 30 mm in Y, and less than 20 mm in Z.
 13. The headmounted display device of claim 12, wherein the reflective opticalsurface of the first and third mirrors is a concave reflective opticalsurface and the reflective optical surface of the second mirror is aconvex reflective optical surface.
 14. A micro-display alignmentmechanism configured to be mounted to a structural frame of a headmounted display device, the structural frame arranged generally along aX-axis and a Y-axis for viewing along a Z-axis, the X, Y, and Z axesbeing mutually perpendicular, the micro-display alignment mechanismcomprising: a micro-display holder configured to hold a micro-display;and a carriage configured to couple to and constrain motion of themicro-display holder to motion along the X and Z axes and restrainingrotational motion of the micro-display holder to align and control areflectively guided light ray bundle from the micro-display to a user'seye by positioning the micro-display along the X and Z axes, wherein themicro-display holder includes a tab that is received into a slot in thecarriage wherein the tab and slot cooperate to restrain the motion tothe X and Z axes.
 15. The micro-display alignment mechanism of claim 14,comprising: a X-gear including a user-manipulation portion attached to ashaft configured to be received in a first opening in the carriage; anda Z-gear including a user-manipulation portion attached to a shaftconfigured to be received in a second opening in the carriage.
 16. Themicro-display alignment mechanism of claim 15, wherein: themicro-display holder includes upwardly extending teeth; and the X-gearshaft is configured to insert into the first opening of the carriagealong the Z-axis and includes radially extending teeth to engage theupwardly extending teeth of the micro-display holder to translaterotational motion of the X-gear shaft to linear motion of themicro-display along the X-axis.
 17. The micro-display alignmentmechanism of claim 15, wherein: the micro-display holder includesdownwardly extending teeth; and the Z-gear shaft is configured to insertinto the second opening of the carriage along the X-axis and includesradially extending teeth to engage the downwardly extending teeth of themicro-display holder to translate rotational motion of the Z-gear shaftto linear motion of the micro-display along the Z-axis.
 18. A method ofassembling a micro-display mechanism configured to be mounted to astructural frame of a head mounted display device, the structural framearranged generally along a X-axis and a Y-axis for viewing along aZ-axis, the X, Y, and Z axes being mutually perpendicular, the methodcomprising: attaching a micro-display to a first portion of amicro-display holder, assembling a second portion of the micro-displayholder to a carriage configured to couple to and constrain motion of themicro-display holder to motion along the X and Z axes and restrainingrotational motion of the micro-display holder to align and control areflectively guided light ray bundle from the micro-display to a user'seye by positioning the micro-display along the X and Z axes, wherein themicro-display holder includes a tab that is received into a slot in thecarriage wherein the tab and slot cooperate to restrain the motion tothe X and Z axes; providing a X-gear including a user-manipulationportion attached to a shaft; inserting the X-gear shaft into a firstopening in the carriage; providing a Z-gear including auser-manipulation portion attached to a shaft; and inserting the Z-gearshaft into a second opening in the carriage.